/LINES_PER_PAGE=n

    Specifies, with the value n, the number of lines of index entries
    on each page of the finished index. This number does not include
    the number of lines required for running heads and feet.

    The default is 55 lines. This value is designed to work properly
    in the default formatting environment of DSR. You must calculate
    the value n if you change the default environment in any of the
    following ways:

    o  If you use subtitles in the document that requires the .RNX
       file.

    o  If you make the page length for the document anything other
       than 58 lines per page.

    o  If you use any .LAYOUT command other than zero.

    To calculate the correct value for the /LINES_PER_PAGE qualifier,
    use the following formula:

    /LINES_PER_PAGE=n
    n = .PAGE SIZE ( the first parameter is length value)
        minus 4 if subtitles are used, minus 3 if no subtitles
        minus the number of lines reserved for .LAYOUT 1,
              .LAYOUT 2, or .LAYOUT 3.